DESCRIPTION (Applicant's abstract): Adults with mental illness who have a comorbid substance use disorder represent a major public health problem. From a public health perspective, the presence of a substance use disorder co-existing with mental illness is likely to increase (1) the difficulty of providing effective psychiatric treatment efficiently; (2) the seriousness of medical problems (secondary to the combination of these two disorders) that might otherwise be avoided or respond better to treatment; and (3) the rate of mortality. These three problems, higher psychiatric treatment costs, increased medical morbidity and excess mortality in mentally ill patients with comorbid substance use, are not new subjects for study, but no previous research has examined the interrelationship of all three problems. The studies we have reviewed are limited in two ways: (1) they address only one or at most two of the three problems and (2) they are potentially biased because they are limited to small, clinically homogeneous samples at a single point in time (e.g., adults with schizophrenia on admission to a psychiatric hospital). This suggests a need for sampling from a broader spectrum of mental disorders, increasing the size of the sample so that there is adequate power to detect differences in medical disorders that occur with low frequency, using a larger window of time to identify cases and sampling from cases treated in both inpatient and outpatient settings. Using 1995 data from the Massachusetts Medicaid and Department of Public Health, we propose to compare the one-year prevalence of substance use, medical disorders and mortality using a three x two design, classifying enrollees on two dimensions: mental status (psychotic disorder, non-psychotic disorder, and no mental disorder) and substance use disorder (yes, no). We propose to answer the following questions: What are the patterns of care and treatment costs for psychiatric disorders in the four groups of adults treated for mental illness? How does the treated prevalence and severity of medical disorders vary among these groups? What are the most common causes of death for each group? What is the mortality rate for each group?